JPH0686362U - External cavity structure of single mode continuous wave laser. - Google Patents

Abstract

(57) [Summary] [Object] To provide an external resonator structure for a single-mode continuous-wave laser in which the wavelength width of the continuous-wave laser is widened by performing initial fine adjustment with a diffraction grating. [Structure] A fixed plate 1 arranged on a horizontal plane, a link 2 rotating around a point C, an end point B moving on the fixed plate 1 toward a point C, and rotatable with a link 2 at a midpoint D. A link 3 to be connected, and a diffraction grating 4 held at the end point A,
The laser diode 5 which is arranged so that its optical axis is aligned with a straight line AC connecting the end points A and C, and which emits laser light to the diffraction grating 4, and the optical axis is aligned with the straight line AC direction, is installed between the straight lines AC. The lens 6, the lens 7 installed in the direction opposite to the lens 6 with respect to the laser diode 5 with the optical axis aligned with the straight line AC direction, and the isolator 8 installed at a position where the laser light is extracted via the transmitted light lens 7. And an optical output fiber 9 connected to the isolator 8.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an external resonator structure capable of producing a single-mode continuous-wave laser with a wide and tunable wavelength.

[0002]

[Prior art]

 This type of external resonator structure is known as that described in "ELECTRONICS LETTERS 17th January 1991, vol. 27, No. 2, pp 183-184".

This configuration will be described with reference to FIGS. 3 and 4. Reference numeral 11 denotes a fixed plate, and a plate 12 that can move in parallel in the direction of the straight line AC is installed on the fixed plate 11. The rotating rod 13 rotates on the plate 12 about the point A, and the end point B of the rotating rod 13 moves in the direction BC while always contacting the upper surface of the plate 16 when the plate 12 moves. The diffraction grating 14 is fixed to the end point A of the rotary rod 13 with its surface aligned with the straight line AB direction. The plate 16 is fixed on the fixing plate 11 with its upper surface aligned with the BC direction. The spring 15 is attached between the fixed point E of the plate 11 and the end D of the rotary rod 13.

The AR-coated laser diode 17 is fixed on the fixing plate 11 by aligning the surface C (the surface not coated with AR) with the BC direction and the optical axis with the AC direction. The lens 18, the isolator 19 and the optical output fiber 20 are fixed on the plate 11 in the opposite direction with respect to the laser diode 17 together with the optical axis of the laser diode 17.

Due to the tension of the spring 15, the terminal B of the rotating rod 13 always contacts the upper surface of the plate 16. When the plate 12 is moved up and down, the distance L between the point A and the point C and the incident / emission angle θ 2 change at the diffraction grating 14.

When the laser diode 17 is in the emitting state, the laser resonates through the lens 18 between the surface C of the laser diode 17 and the diffraction grating 14. The frequency of the oscillation laser and the intensity of the laser depend on the distance L and the angle θ of the diffraction grating 14.

Here, when the angle θ is not zero, single mode oscillation is possible, and the relationship between the interval L and the angle θ must follow the formula L / sin θ = constant in order to oscillate with a continuous wave length. I won't.

In the structure shown in FIG. 3, L / sin θ = AB = constant from the geometrical relationship shown in FIG. 4, and the single mode continuous oscillation condition is satisfied. By moving the plate 12 up and down in parallel, the distance L = AC changes, and the resonant optical frequency continuously changes between ACs. By the way, part of the laser is transmitted from the end face C of the laser diode 17, enters the optical output fiber 20 through the isolator 19, and is extracted as output light.

In principle, this system can adjust the frequency of a single mode continuous wave laser to any value. However, in practice, it is necessary to finely adjust the direction of the upper surface of the plate 16 in order to cause oscillation first, so that the range in which the optical frequency shifts is limited. Further, another problem is that the range of the continuous oscillation frequency becomes narrow if the direction of parallel movement of the plate 12 deviates from the optical axis of the laser diode 17 even a little.

[0010]

[Problems to be solved by the device]

 In the configuration as shown in FIG. 3, since the plate 16 must first be tilted and adjusted to cause oscillation, the wavelength width of the continuous wave laser is shortened, and the moving direction of the plate 12 is changed to the optical axis of the laser. It is difficult to adjust to, and it may adversely affect the working of the composition.

The present invention was made in order to solve the above-mentioned problems, and a single mode continuous wave laser in which the wavelength width of the continuous wave laser is widened by performing initial fine adjustment with a diffraction grating. It is an object to provide an external resonator structure.

[0012]

[Means for Solving the Problems]

 In order to achieve the above object, in the present invention, a fixed plate 1 arranged on a horizontal plane, a first link 2 rotating around a point C on the fixed plate 1, and a first end point B are fixed. The second link 3 moving on the plate 1 towards the point C and rotatably connected to the first link 2 at the midpoint D, and the diffraction held at the second end point A of the second link 3. The grating 4 and the AR coating laser diode 5 for arranging the optical axis on the straight line AC connecting the end points A and C to emit laser light to the diffraction grating 4 and the optical axis are aligned with the straight line AC direction. The first lens 6 installed between the straight lines AC, the second lens 7 installed in the direction opposite to the lens 6 with respect to the AR coating laser diode 5 with the optical axis aligned with the straight line AC direction, and the laser light Eye installed at the position where it is taken out through the transmitted light lens 7 of It comprises a regulator 8, and an optical output fiber 9 connected to the Asoireta 8.

[0013]

[Action]

 Next, the operation of the external cavity of the continuous wave laser according to the present invention will be described with reference to FIG. Reference numeral 1 is a fixed plate, 2 and 3 are links, 4 is a diffraction grating, 5 is an AR coating diode, 6 and 7 are lenses, 8 is an isolator, and 9 is an optical output fiber.

In FIG. 1, the link 2 is rotatably connected to the fixed plate 1 at an end C, and is rotatably connected to the link 3 at an end D opposite to the end C. The axis of rotation is perpendicular to the plane of FIG. A point D is a midpoint between both ends A and B of the link 3, and the end point B moves left and right on the fixed plate 1.

The surface of the diffraction grating 4 is aligned with the straight line AB and is fixed on the link 3. The end surface of the AR coating diode 5 is aligned with the CB direction, and the optical axis is aligned with the AC direction. The lenses 6 and 7 are aligned with the optical axis of the AR coating diode 5. The optical axis of the isolator 8 is aligned with the optical axis of the AR coating diode 5. Further, the diffraction grating 4 is installed so that it can be slightly rotated about the end point A of the link 3.

Next, the operation of the system shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a diagram showing the geometric movement of FIG. In FIG. 2, DC = DA = DB, and the line AC and the line CB are orthogonal to each other. When the point B is moved to the point B ', the point A moves on the AC straight line and moves to the point A'. The resonance phenomenon of the laser between the diffraction grating 4 and the laser diode 5 is similar to the conventional one.

[0017]

【Example】

 FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

By using the fixed plate 1, the link 2 can be freely rotated by connecting it to the point C of the fixed plate 1 and the midpoint D of the link 3 (the rotation axis is perpendicular to the paper surface). The link 3 has its end B moved on the fixed plate 1 in the BC direction and is connected to the link 2 at the midpoint D. The diffraction grating 4 has its surface aligned in the AB direction and is fixed at a point A of the link 3. The AR coating laser diode 5 is fixed on the plate 1 with its optical axis aligned with the AC direction and with the surface C (the surface not coated with AR) aligned with the BC direction. The lenses 6, 7 and the isolator 8 and the optical output fiber 9 are fixed to point C as shown in FIG. 1 by aligning the optical axis with the optical axis of the laser diode 5.

Next, the operating principle will be described.

(1) Oscillation Wavelength Value of Fabry-Perot Interferometer The resonance wavelength value at which the laser is excited between the reflecting surfaces to resonate is shown in the following expression (1).

2nL = m ₁ · λ ₁ (1) where m ₁ = natural number of 1, 2, 3, λ ₁ = oscillation wavelength value, L = interval between reflecting surfaces, n = reflection It is the refractive index between the surfaces. Substituting the band of L = 50 mm, n = 1, and λ = 1500 nm in the equation 1, the equation 1 becomes 2nL = (m ₁ −1) λ ₁ = m ₁ λ ₁ ′. That is, Δλ ₁ = λ ₁ / m ₁ = (λ ₁ ) ² / 2nL = (λ ₁ ) ² / 2L, Δλ ₁ = 2.25 × 10 ⁻⁵ μm (Δf ₁ = 2.8 GHz). The waveform is shown.

(2) Diffraction of Diffraction Grating As in the configuration shown in FIG. 1, the laser travels in the same direction and then returns, so that the incident angle and the emission angle with respect to the diffraction grating 4 become equal. In this case, the wavelength value that can be emitted by the diffraction of the diffraction grating 4 is represented by the following equation (2).

K λ ₂ = 2d sin θ (2) where K = diffraction order, λ ₂ = emission wavelength, d = slot spacing of the diffraction grating, and θ = incidence / emission angle. Assuming that K = 1, λ ₂ = 1500 to 1600 nm and d = 1.67 μm (600 lines / 1 mm diffraction grating) in the formula (2), θ (1500 nm) = 26.7 ° θ (1600 nm) = 28.6 ° Δθ = 1.9 ° vs. Δλ = 100 nm.

(3) Continuous oscillation When L is changed so that m ₁ does not change in the equation (1), λ ₁ changes correspondingly as in the following equation (3).

Dλ ₁ / λ ₁ = dL / L Equation (3) When θ is changed so that K does not change in Equation (2), the emission wavelength value λ ₂ changes as in the following Equation (4).

Dλ ₂ / λ ₂ = d (sinθ) / sinθ (4) The configurations shown in FIGS. 1 and 2 show the following relationship. L / sin θ = AB = constant, that is, the following equation (5) is derived.

DL / L = d (sin θ) / sin θ ... Formula (5) From Formula (3), Formula (4), and Formula (5), dλ ₁ / λ ₁ = dλ ₂ / λ ₂ is established. That is, the following equation (6) is established.

[0028] also dλ ₁ / λ ₁ = constant ...... formula (6) (1) λ ₂ According to the example of the oscillation wavelength value of the Fabry-Perot interferometer shown to have any value, | λ ₂ -λ ₁ | When ≦ Δλ _1/2 and λ ₂ is larger than λ ₁ , the following equation (7) is established.

The _{λ 2 / λ 1 ≦ (λ} 1 + Δλ 1/2) / λ 1 = 1 + Δλ 1 / 2λ 1 ...... formula (7) (6) and the following relationship from the expression (7) is guided.

Λ ₂ / λ ₁ = (λ ₂ ) ′ / (λ ₁ ) ′ ≦ 1 + Δλ ₁ / 2λ ₁ {(λ ₂ ) ′ − λ ₂ } / {(λ ₁ ) ′ − λ ₁ } ≦ 1 + Δλ ₁ / 2λ ₁ {(λ ₂ ) ′-(λ ₁ ′)}-(λ ₂ −λ ₁ ) ≦ {Δλ ₁ / 2λ ₁ } {(λ ₁ ) ′-λ ₁ } {(λ ₂ ) ′-( λ ₁ ′)} − (λ ₂ −λ ₁ ) is λ ₂ , and (λ ₂ ) ′ shows a relative shift to the values of λ ₁ and (λ ₁ ) ′. If is smaller than Δλ _{1/2, the} laser can be resonated, and the following equation (8) is established.

The _{Δλ 1/2 ≦ {Δλ 1} / 2λ 1} {(λ 1) '- λ 1} ...... (8) that _{is, (λ 1)' - λ} 1 ≧ λ 1 or, (lambda ₁₎ ′ ≧ 2λ ₁ holds.

In the present invention, in the configuration as shown in FIG. 1, the initial adjustment is necessary to keep the wavelength value λ _{2 at the} point M in FIG. 5A, so fine adjustment is performed at the angle θ of the diffraction grating 4. When the point B is moved on the straight line CB, the values of λ ₁ and λ ₂ change simultaneously. By moving the point B to the right lambda ₁ value approaches the lambda ₁ 'value. At the same time, the λ ₂ value approaches the λ ₂ ′ value (point N). That is, the relative movement for the λ ₂ value vs. λ ₁ value or the (λ ₂ ) ′ vs. (λ ₁ ) ′ value is as shown in FIG. 5B. During this period, the MN always satisfies the oscillation condition, and therefore the wavelength width (λ ₁ ) ′ − λ ₁ = λ ₁ is the geometric continuous wave wavelength width. That is, in the case of the wavelength band of 1.5 μm, the continuous oscillation wavelength width is geometrically 1.5 μm by this configuration and the adjusting method.

[0033]

[Effect of device]

 According to the present invention, the variable wavelength width of a geometric continuous-wave laser becomes much wider than that of a conventional external resonator.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an external resonator of a laser according to an embodiment of the present invention.

FIG. 2 is a diagram showing the geometrical movement of FIG.

FIG. 3 is a configuration diagram of an external resonator of a conventional laser.

FIG. 4 is a diagram showing the geometrical movement of FIG. 3;

FIG. 5 is an explanatory diagram of a wavelength width of a continuous wave laser.

[Explanation of symbols]

 1 Fixing Plate 2 Link 3 Link 4 Diffraction Grating 5 AR Coating Laser Diode 6 Lens 7 Lens 8 Isolator 9 Optical Output Fiber 11 Fixing Plate

Claims (1)

[Scope of utility model registration request] 1. A fixed plate (1) arranged on a horizontal plane, and a first link which rotates around a point C on the fixed plate (1).
(2) and a second link in which the first end point B moves on the fixed plate (1) toward the point C and is rotatably connected to the first link (2) at the midpoint D. (3), a diffraction grating (4) held at the second end point A of the second link (3), and an optical axis aligned on a straight line AC connecting the end point A and the point C And an AR coating laser diode (5) for emitting laser light to the diffraction grating (4), a first lens (6) installed between the straight lines AC with its optical axis aligned with the straight line AC direction, A second lens (7) installed in a direction opposite to the lens (6) with respect to the AR coating laser diode (5) with its optical axis aligned with the straight line AC direction; 7) and the optical output fiber connected to this isolator (8). Ba (9)
An external cavity structure of a single-mode continuous-wave laser, comprising: